Gets rid of properties defined as both MAKE_SEQ_PROPERTY/MAKE_MAP_PROPERTY, which are just a bad idea. Instead, adds a way for map properties to define a separate "keys" interface.
Fixes: #203
cxx: Fix missing includes masked by composite builds.
misc: Fix typos in comments.
config: Fix missing config forward-declarations.
direct: Adjust Python imports to panda3d.* instead of pandac.*.
display: Split graphicsWindow out into an extension.
framework: Use if/elif/elif/endif instead of ifdef/elif/elif/endif.
ode: Remove erroneous INLINE declarations.
interval: Fix missing import.